The invention relates to eggs and, particularly, to the discovery of an improved technique by processing with minimal denaturation to provide a pasteurized egg product having improved stability during refrigerated storage.
Pasteurization employs the controlled application of heat to reduce the population of microorganisms which affect the preservation of food products, such as eggs. Eggs are particularly susceptible to degradation during heating due to the nature of their protein content. They can easily start to congeal and lose other aspects of functionality. The attainment of a product which is functional and can yet be stored in liquid form has been long sought, especially for low cholesterol egg products which don't contain significant levels of natural yolk.
Most commercial egg pasteurization processes are employed primarily to reduce Salmonella to safe levels while bringing spoilage-promoting organisms to levels most suitable for frozen storage. The products of these processes typically permit one to two weeks stability at refrigerator temperatures (e.g., 0.degree. to 4.degree. C.). Until recently, aseptically-packaged, room-temperature stable eggs or refrigerator-stable eggs were not available on a commercial scale.
In an early advance in egg pasteurization, Lineweaver and Cunningham disclosed in U.S. Pat. No. 3,251,697 that the addition of certain polyvalent metal salts enabled increasing the pasteurization temperature several degrees while not adversely affecting the physical properties of the egg.
This process was confirmed as useful by Strong and Redfern in U.S. Pat. Nos. 3,840,683 and 3,911,144 wherein they disclosed a substantially cholesterol and egg yolk-free frozen egg product which had good freeze-thaw stability. These technologies permitted the marketing and wide availability of a health-oriented product highly desired by many egg lovers. When frozen, the products last for extended times. It would be desirable, however, to improve the stability of such products against spoilage when maintained in a refrigerated condition.
Other early disclosures, primarily for frozen and dry egg products, employ hydrogen peroxide to aid in pasteurization. In both U.S. Pat. No. 2,776,214 to Lloyd et al and U.S. Pat. No. 3,364,037 to Mink et al hydrogen peroxide is added to egg prior to heating. The first of these discloses destroying natural catalase by heating the egg white prior to adding the peroxide. The second adds an alkali. A later patent to Kohl et al (U.S. Pat. No. 3,615,705) combines these two teachings. Peroxide has also been employed as a bleach for fish and other food products, shown for example in U.S. Pat. No. 4,060,644 to Braid. Any oxygen produced by these processes is left with the products, its effect on product quality being unknown or disregarded.
More recently, efforts have been made to produce products which remain stable for extended periods of refrigerated or even room-temperature storage. For example, in U.S. Pat. No. 3,928,632, Glaser and Ingerson disclosed an aseptically-packaged, low cholesterol egg product having an additive emulsion which is separately sterilized and homogenized prior to mixing with an egg component. No details of egg pasteurization are provided, but a lactylate salt is an essential ingredient. Similarly, in U.S. Pat. No. 4,971,827, Huang discloses that high temperatures can be employed when turbulent flow is achieved during pasteurization. It would be desirable to provide long shelf lives and process with minimal equipment fouling.
It would be advantageous to have a procedure for assuring low degrees of denaturation with adequate heat treatment for long-term preservation of egg in liquid form at refrigerator temperatures.